PSI - Issue 16

Eugene Kondryakov et al. / Procedia Structural Integrity 16 (2019) 43–50 Eugene Kondryakov et al. / Structural Integrity Procedia 00 (2019) 000 – 000

49 7

was measured using the optical microscope. Later, the velocities within the regions of the crack propagation, as well as their time and coordinate dependencies, were determined using these time intervals and dimensional coordinates. To build the time dependencies of the velocity of the crack propagation, the moment of the breakout of the first path of the first gauge is taken as the reference point of the time scale. Therefore, the velocities of the crack propagation between each pair of the adjoining gauge paths were determined. The curves of variation of the instantaneous velocity of the crack propagation depending on the time and coordinate were plotted. Fig. 8 shows the variation of the instantaneous velocity of the crack propagation depending on time for standard Charpy specimen. However, there is a drastic jump of velocity up to 1400 m/s in the beginning. Later the velocity decreased to the constant level.

Fig. 8. Variation of the instantaneous velocity of the crack propagation in standard Charpy specimen.

4. Discussion and conclusions

The results of the performed investigations implied that the modern experimental techniques of registration can increase the accuracy and informative nature of the results of impact testing. The use of the specimens of various types and dimensions allows one to evaluate the effect of the scale factor and stress state on the peculiar features of the crack initiation and propagation in the material. The following conclusions can be drawn from the results of investigations: 1. The peculiar features and character of the crack propagation were investigated in standard Charpy specimens, sub-sized specimens and side-grooved specimens during their fracture within the temperature range of - 50...150° С. 2. The high-sensitivity system of registration and methods of quantitative analysis of the macrofracture of the specimens made it possible to obtain the data on the specific energy of deformation and fracture of the specimens of different types, as well as its components: specific energy of the crack initiation, specific energy of ductile crack growth, specific energy of brittle crack jump, and energy of the ductile rupture area. 3. It was established that it is reasonable to use the side-grooved specimens to eliminate the influence of share lips in the determination of various characteristics (energy of the crack propagation, moment of the crack initiation). 4. It was found that the average velocity of the crack propagation in the process of brittle fracture in the zone of the brittle jump in the specimens of various types varies in the range of 100...900 m/s, while in the zone of ductile rupture area – 1...15 m/s. 5. The new data on the variation of the instantaneous velocity of the crack propagation in Charpy specimens made of steel 45 was obtained. The maximum velocity of the crack propagation under impact loading is 1400 m/s.